Efficient formation of stratospheric aerosol for climate engineering by emission of condensible vapor from aircraft

Recent analysis suggests that the effectiveness of stratospheric aerosol climate engineering through emission of non-condensable vapors such as SO₂ is limited because the slow conversion to H₂SO₄ tends to produce aerosol particles that are too large; SO₂ injection may be so inefficient that it is difficult to counteract the radiative forcing due to a CO₂ doubling. Here we describe an alternate method in which aerosol is formed rapidly in the plume following injection of H₂SO₄, a condensable vapor, from an aircraft. This method gives better control of particle size and can produce larger radiative forcing with lower sulfur loadings than SO₂ injection. Relative to SO₂ injection, it may reduce some of the adverse effects of geoengineering such as radiative heating of the lower stratosphere. This method does not, however, alter the fact that such a geoengineered radiative forcing can, at best, only partially compensate for the climate changes produced by CO₂.